I have a custom chopper bike. thinking about adding one of these engines, but i think im gonna have a bit of trouble because of my back disk break. any help would be appretated
I think you'll have more problems with the motor mount than the sprocket on the rear. The sprocket can be taken care of with a Top Hat adapter from King's.
If you don't view the motor mount as a problem (many here won't), then you got your work cut out for ya!